Color negative photographic elements are conventionally formed with superimposed blue, green and red recording layer units coated on a support. The blue, green and red recording layer units contain radiation-sensitive silver halide emulsions that form a latent image in response to blue, green and red light, respectively. Additionally, the blue recording layer unit contains a yellow dye image-forming coupler, the green recording layer unit contains a magenta dye image-forming coupler, and the red recording layer unit contains a cyan dye image-forming coupler. Following imagewise exposure, the photographic elements are processed in a color developer, which contains a color developing agent that is oxidized while selectively reducing to silver latent image-bearing silver halide grains. The oxidized color developing agent then reacts with the dye image-forming coupler in the vicinity of the developed grains to produce an image dye. Yellow (blue-absorbing), magenta (green-absorbing) and cyan (red-absorbing) image dyes are formed in the blue, green and red recording layer units respectively. Subsequently the element is bleached (i.e., developed silver is converted back to silver halide) to eliminate neutral density attributable to developed silver and then fixed (i.e., silver halide is removed) to provide stability during subsequent room light handling.
When processing is conducted as noted above, negative dye images are produced. To produce a viewable positive dye image and hence to produce a visual approximation of the hues of the subject photographed, white light is typically passed through the color negative image to expose a second color photographic element having blue, green and red recording layer units as described above, usually coated on a white reflective support. The second element is commonly referred to as a color print element, and the process of exposing the color print element through the image-bearing color negative element is commonly referred to as printing. Processing of the color print element as described above produces a viewable positive image that approximates that of the subject originally photographed.
A problem with the accuracy of color reproduction delayed the commercial introduction of color negative elements. In color negative imaging two dye image-forming coupler containing elements are exposed and processed to arrive at a viewable positive image. The dye image-forming couplers each produce dyes that only approximate an absorption profile corresponding to that recorded by the silver halide grains. Since the color negative element cascades its color errors forward to the color print element, the cumulative error in the final print is unacceptably large, absent some form of color correction.
A commercially acceptable solution that remains in use today in the form of color slides is to subject a color photographic element having blue, green and red recording layer units to reversal processing. In reversal processing the film is first black-and-white processed to develop exposed silver halide grains imagewise without formation of a corresponding dye image. Thereafter, the remaining silver halide grains are rendered developable. Color development followed by bleaching and fixing produces a viewable color image corresponding to the subject photographed. The primary objections to this approach are (a) the more complicated processing required and (b) the absence of an opportunity to correct underexposures and overexposures, as is provided during exposure of a print element.
Commercial acceptance of color negative elements occurred after commercial introduction of the first color reversal films. The commercial solution to the problem of cascaded color error has been to place colored masking couplers in the color negative element at concentrations of greater than 0.12 (typically greater than 0.25) millimole/m.sup.2. Illustrations of colored masking couplers are provided by Research Disclosure, Vol. 389, September 1996, Item 38957, XII. Features applicable only to color negative, paragraphs (1) and (2). The colored masking couplers lose or change their color in areas in which grain development occurs producing a dye image that is a reversal of the unwanted absorption of the image dye. This has the effect of neutralizing unwanted spectral absorption by the image dyes by raising the neutral density of the processed color negative element. In practical applications this is not a difficulty, since increased neutral minimum densities are easily offset by increasing exposure levels when exposing the print element through the color negative element.
In color negative films in which silver coating coverages are significantly reduced it is in some instances difficult to obtain a desired level of image descrimination (D.sub.max -D.sub.min) when masking couplers are present. The following patents include examples of color negative films in which masking couplers have been omitted: Schmittou et al U.S. Pat. No. 5,183,727 (Element I), Sowinski et al U.S. Pat. Nos. 5,219,715 and 5,322,766 (Element III), English et al U.S. Pat. No. 5,318,880 (Sample 108), and Szajewski et al U.S. Pat. No. 5,298,376 (Samples 301 and 302). In limiting silver coating coverages these patents have not exhibited the degree of exposure latitude normally desired for color negative films.
It should be noted that colored masking couplers have no applicability to reversal color elements intended for direct viewing. They actually increase visually objectionable dye absorption in a color negative film, super-imposing an overall salmon colored tone, which can be tolerated only because color negative images are not intended to be viewed. On the other hand, color reversal images are made to be viewed, but not printed. Thus colored masking couplers, if incorporated in reversal films, would be visually objectionable and serve no useful purpose.
In addition to incorporating colored masking couplers in color negative photographic elements it has been recognized that improved dye images can be realized by incorporating one or more developer inhibitor releasing compounds in the dye image-forming layer units. The development inhibitor, which increases in mobility by release during color development, improves the dye image by interacting with adjacent layer units to create favorable interimage effects and by sharpening dye image edge definition. Illustrations of development inhibitor releasing compounds are provided by Research Disclosure, Item 38957, cited above, X. Dye image formers and modifiers, C. Image dye modifiers.
Selection of suitable DIR compounds based on a measured diffusion factor is illustrated by Iwasa et al U.S. Pat. No. 4,524,130. Iwasa et al addresses the problem of providing color negative photographic elements that provide improved color print enlargements. The problem is addressed by employing in combination radiation-sensitive silver halide emulsion layers differing in iodide content and containing DIR's having diffusion factors of 0.4 or higher. Iwasa et al makes no mention of adapting color negative photographic elements for producing images that are of improved quality when converted to digital form and then reconstructed for viewing.
Techniques for scanning color negative films to obtain viewable images are well known, as illustrated by Giorgianni et al U.S. Pat. No. 5,267,030 and Bohan et al U.S. Pat. No. 5,698,379.